Popocatepetl ("The Smoking mountain" in Nahuatl languaje) is a strato volcano, 5450 m high, located in central Mexico at Lat. N. 19.02° and Long. W. 98.62° It is distant 60 km East from Mexico City and 30 km West from the city of Puebla. An estimated population of close to 500 000 people live in the vicinity of the volcano. The last eruptions in this century occurred in 1919 to 1927, in December 1994 and again in March 1996.

OBSERVATORY

Popocatepetl Volcanological Observatory (POVO) was founded in July 1994 just before the beginning of its eruptive activity in December that same year. It was basically established for surveillance and monitoring of the volcano through a dense instrumental network designed to permanently observe its activity and automatically detect any volcanic unrest which in turn would lead to adopt safety measures and if necessary, activate a pre-established emergency plans. The observatory is operated and supported by CENAPRED (The National Center of Disaster Prevention, depending on the Ministry of the Interior) in collaboration with several research institutions.

POVO is comprised of a network of 15 remote field stations installed around the volcano at altitudes ranging from 2500 to 4200m, and a main recording and processing center located at CENAPRED in Mexico City. The closest stations are 2.5 km from the crater. The instrumentation consists of: 14 short-period seismometers (10 of them triaxial), 1 intermediate triaxial period seismometer, 3 triaxial broadband seismometers, 4 biaxial bubble-type tiltmeters, and one video camera for real time visual observations of the volcano. These instruments generate close to 50 different signals which, by means of a complex radio communication network, are continuously telemetered to the central recording station.

In addition, the signals from two remote seismic stations, one located half way to the Pacific Coast and the other close to the Citlaltepetl volcano East of Puebla, are also telemetered to CENAPRED. These signals allow discrimination of regional and volcanic seismicity.

Seismic and tilt data are continuously processed and displayed through a local computer network. Two independent data acquisition systems record all signals and special software packages detect and processes the main seismic events. Finally all information is concentrated and stored in a data bank and later analyzed by other scientists and stored. Seismic activity of the most important stations is also continuously recorded on ten drum recorders for immediate visual inspection.

All the information from the network is analyzed on a daily basis and major seismic events manually processed and located. A summary of the seismic activity is reported each week in a special bulletin.

Any increase of its activity is automatically detected by an alarm system which locally alerts personnel in charge with an audible alarm signal and through an autodial system sends prerecorded messages to assigned home telephones and paging devices.

Government authorities and civil protection officials are routinely informed about the level of activity of the volcano by means of specially designed reports. Upon the occurrence of a major event, immediate reports and recommendations are issued.

OTHER MEASUREMENTS AND OBSERVATIONS

Frequent helicopter flights over the crater and around the volcano, allow observations of its interior and any abnormal feature related to its activity. Photographic records are kept of each flight. Periodic high resolution aerial photographs are also taken.

In addition to continuous tilt monitoring, frequent geodetic measurements are also made with conventional laser EDM’s and two GPS receiving stations.

Volcanic gases, in particular sulfur dioxide is routinely measured with a COSPEC instrument. Two to three ground-based measurements of the gas volume emitted by the volcano are made each week. Special airborne measurements are done when aircrafts are available.

Ash particles and other volcanic materials are chemically and petrologically analyzed in special laboratories at UNAM.